Vacume tube TC

I've been tinkering around with a vaccume tube coil now for several months
using a pair of 811a's (triodes) and was able to produce a nice 3" brush
discharge off the top of the coil ( tall thin candlestick variety).  I then
switched to a 4-500z with the intent to produce greater output....
Unfortuneately, the same circuit doesn't produce *any* brush output, although
if I get a flourescent tube near to the primary and secondary it lights up so
there must be output of a sort.  I have heard it speculated that the extra
controll grid in the 4-500z is causing the problem and that what I really
need is a 3-500z triode.

Does anyone have any ideas or suggestion about this?